Vacuum distillation is a well-known process for separating chemical components on the basis of differences in vapor pressure.
Distillation under vacuum has several advantages over distilling at atmospheric or superatmospheric pressures, because of the lower temperatures at which the process can be conducted. Economical low-grade heat sources may be used. Safety is enhanced by the low temperature operation, and thermal degradation of the chemical components is minimized. Furthermore, leaching of impurities from the walls of the apparatus itself is minimized. Some of the best materials of construction, such as polyethylene, cannot be used at the higher temperatures but work well at the temperatures of vacuum distillation.
A vacuum distillation apparatus which works well in areas of limited headroom was patented by Applicant in U.S. Pat. No. 4,444,623 hereby incorporated by reference. A shortcoming of this invention which required the distillate pump was overcome by the vacuum distillation apparatus patented by Applicant in U.S. Pat. No. 4,762,593 incorporated above by reference. A shortcoming of that apparatus is the circulation of fluid from two or more stages in series. This requires precise control of pumps circulating the fluid to ensure that the fluid level in the condensation chambers remains within relatively close limits. If the levels were to fall below the level of tubes extending downward into the chambers the vacuum for that chamber would be bypassed causing operation of the apparatus to cease. This precise control requires relatively sophisticated apparatus such as electronic sensors and flow control valves. Eliminating this pumping requirement and associated apparatus would simplify and improve the apparatus considerably.